Changes in surface stress of platinum electrode in acidic and alkaline sulfate or alkaline fluoride solutions

The changes in surface stress of a platinum electrode in acidic and alkaline sulfate or alkaline fluoride solutions were measured by the bending-beam method in connection with the surface oxygenation reaction of platinum. The surface stress exhibited a maximum in the electrical double layer potential region of platinum. The potential of the surface stress maximum obtained in the anodic potential sweep showed the dependence of -40 mV/pH in acidic sulfate solution and of 290 mV/pH in alkaline sulfate and fluoride solutions, respectively, indicating the strong specific adsorption of OH- ion on platinum in alkaline solutions. It was found that the derivative of surface stress with electrode potential showed a maximum in the potential range corresponding to the onset of the surface oxygenation reaction for formation of PtOHad and deviated upward from the surface charge density estimated from the cyclic voltammogram. The potential at which the derivative of surface stress with electrode potential showed a maximum, gave a dependence of 268 mV/pH over a wide pH range, irrespective of the anionic species (sulfate or fluoride ions). It has been pointed out that the difference between the derivative of surface stress with electrode potential and the surface charge density increases when the surface charge transfer reaction of an adsorbed ion such as surface oxygenation reaction takes place on a noble metal. (C) 2003 The Electrochemical Society.